7 files changed, 73 insertions, 1 deletions
diff --git a/include/clang/Basic/Attr.td b/include/clang/Basic/Attr.td
index 441a79a23b..25c9fcb5af 100644
--- a/include/clang/Basic/Attr.td
+++ b/include/clang/Basic/Attr.td
@@ -948,6 +948,10 @@ def ForceInline : InheritableAttr {
   let Spellings = [Keyword<"__forceinline">];
 }
 
+def SelectAny : InheritableAttr {
+  let Spellings = [Declspec<"selectany">];
+}
+
 def Win64 : InheritableAttr {
   let Spellings = [Keyword<"__w64">];
 }
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index f5345eb8c3..b770c07339 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1948,6 +1948,8 @@ def warn_weak_identifier_undeclared : Warning<
   "weak identifier %0 never declared">;
 def err_attribute_weak_static : Error<
   "weak declaration cannot have internal linkage">;
+def err_attribute_selectany_non_extern_data : Error<
+  "'selectany' can only be applied to data items with external linkage">;
 def warn_attribute_weak_import_invalid_on_definition : Warning<
   "'weak_import' attribute cannot be specified on a definition">,
   InGroup<IgnoredAttributes>;
diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 0b03a3c4b6..b3b05199a5 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -1900,7 +1900,13 @@ CodeGenModule::GetLLVMLinkageVarDefinition(const VarDecl *D,
     return llvm::Function::DLLImportLinkage;
   else if (D->hasAttr<DLLExportAttr>())
     return llvm::Function::DLLExportLinkage;
-  else if (D->hasAttr<WeakAttr>()) {
+  else if (D->hasAttr<SelectAnyAttr>()) {
+    // selectany symbols are externally visible, so use weak instead of
+    // linkonce.  MSVC optimizes away references to const selectany globals, so
+    // all definitions should be the same and ODR linkage should be used.
+    // http://msdn.microsoft.com/en-us/library/5tkz6s71.aspx
+    return llvm::GlobalVariable::WeakODRLinkage;
+  } else if (D->hasAttr<WeakAttr>()) {
     if (GV->isConstant())
       return llvm::GlobalVariable::WeakODRLinkage;
     else
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index e0e8bd646b..03e9afc002 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -4638,6 +4638,15 @@ static void checkAttributesAfterMerging(Sema &S, NamedDecl &ND) {
       ND.dropAttr<WeakRefAttr>();
     }
   }
+
+  // 'selectany' only applies to externally visible varable declarations.
+  // It does not apply to functions.
+  if (SelectAnyAttr *Attr = ND.getAttr<SelectAnyAttr>()) {
+    if (isa<FunctionDecl>(ND) || !ND.isExternallyVisible()) {
+      S.Diag(Attr->getLocation(), diag::err_attribute_selectany_non_extern_data);
+      ND.dropAttr<SelectAnyAttr>();
+    }
+  }
 }
 
 /// Given that we are within the definition of the given function,
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 7b3345a332..ddcbafc30a 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -4683,6 +4683,16 @@ static void handleForceInlineAttr(Sema &S, Decl *D, const AttributeList &Attr) {
     S.Diag(Attr.getLoc(), diag::warn_attribute_ignored) << Attr.getName();
 }
 
+static void handleSelectAnyAttr(Sema &S, Decl *D, const AttributeList &Attr) {
+  if (!checkMicrosoftExt(S, Attr))
+    return;
+  // Check linkage after possibly merging declaratinos.  See
+  // checkAttributesAfterMerging().
+  D->addAttr(::new (S.Context)
+             SelectAnyAttr(Attr.getRange(), S.Context,
+                           Attr.getAttributeSpellingListIndex()));
+}
+
 //===----------------------------------------------------------------------===//
 // Top Level Sema Entry Points
 //===----------------------------------------------------------------------===//
@@ -4909,6 +4919,9 @@ static void ProcessInheritableDeclAttr(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_ForceInline:
     handleForceInlineAttr(S, D, Attr);
     break;
+  case AttributeList::AT_SelectAny:
+    handleSelectAnyAttr(S, D, Attr);
+    break;
 
   // Thread safety attributes:
   case AttributeList::AT_GuardedVar:
diff --git a/test/CodeGen/ms-declspecs.c b/test/CodeGen/ms-declspecs.c
index 26bdc58ebb..5dc7787b8f 100644
--- a/test/CodeGen/ms-declspecs.c
+++ b/test/CodeGen/ms-declspecs.c
@@ -1,5 +1,10 @@
 // RUN: %clang_cc1 -triple i386-pc-win32 %s -emit-llvm -fms-compatibility -o - | FileCheck %s
 
+__declspec(selectany) int x1 = 1;
+const __declspec(selectany) int x2 = 2;
+// CHECK: @x1 = weak_odr global i32 1, align 4
+// CHECK: @x2 = weak_odr constant i32 2, align 4
+
 struct __declspec(align(16)) S {
   char x;
 };
diff --git a/test/SemaCXX/attr-selectany.cpp b/test/SemaCXX/attr-selectany.cpp
new file mode 100644
index 0000000000..0f9776dbf5
--- /dev/null
+++ b/test/SemaCXX/attr-selectany.cpp
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -fms-extensions -fsyntax-only -verify %s
+// MSVC produces similar diagnostics.
+
+__declspec(selectany) void foo() { } // expected-error{{'selectany' can only be applied to data items with external linkage}}
+
+__declspec(selectany) int x1 = 1;
+
+const __declspec(selectany) int x2 = 2; // expected-error{{'selectany' can only be applied to data items with external linkage}}
+
+extern const __declspec(selectany) int x3 = 3;
+
+extern const int x4;
+const __declspec(selectany) int x4 = 4;
+
+// MSDN says this is incorrect, but MSVC doesn't diagnose it.
+extern __declspec(selectany) int x5;
+
+static __declspec(selectany) int x6 = 2; // expected-error{{'selectany' can only be applied to data items with external linkage}}
+
+// FIXME: MSVC accepts this and makes x7 externally visible and comdat, but keep
+// it as internal and not weak/linkonce.
+static int x7; // expected-note{{previous definition}}
+extern __declspec(selectany) int x7;  // expected-warning{{attribute declaration must precede definition}}
+
+int asdf() { return x7; }
+
+class X {
+ public:
+  X(int i) { i++; };
+  int i;
+};
+
+__declspec(selectany) X x(1);